Mixed outbreak of parainfluenza type 1 and influenza B associated with tourism and air travel

Abstract

Background: A preseasonal outbreak of influenza-like illness was reported in a tourist group that had returned from Ireland to the United States on October 1 and 2, 1999. The authors investigated to determine the timing, extent, and nature of the outbreak. Methods: A cohort study was conducted among the entire group. Cases were defined as illness occurring among tour members who experienced cough or sore throat with onset from September 29 through October 5. Nasopharyngeal and throat cultures were examined for respiratory viruses. Results: Eighteen (60%) of the 30 tourists were ill; the majority (66%) of cases had onset of illness within 1 day of departure from Ireland. Human parainfluenza virus type 1 was isolated from six cultures, and influenza B from three. The attack rate was 100% among the eight persons 65 years of age or older versus 45% among the 22 persons younger than 65 years (P = 0.01). Conclusion: International travellers, particularly older persons and members of organized tour groups, may experience increased risks for respiratory viral infection. and containment of imported infectious diseases depend on prompt reporting and epidemiologic investigation.